震源近くでの長周期地震波の観測

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書誌事項

タイトル別名
  • Observation of Long-Period Seismic Waves at a Short Distance from the Focal Area
  • シンゲン チカク デ ノ チョウ シュウキ ジシンハ ノ カンソク

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抄録

A wide band seismograph system of portable type was devised to make the temporary observation of long-period seismic waves easily. This system consists of an electromagnetic seismometer with pendulum of 1.0Hz, electrical R-C integrating circuit, IC operational amplifiers, and a long term data recorder. In order to get a broad frequency response curve and a large dynamic range for seismic waves from 0.1 to 100Hz, the output of this system was recorded on the magnetic tape, being deviled into the three channels named LONG, MIDDLE and SHORT, respectively.<br>An earthquake of magnitude 6.0 occurred in the east of Fukui Prefecture on August 31, 1972. Three temporary array stations with the wide band seismograph systems were set up at a short distance from the focal area. Eight aftershocks (2.15≤M≤4.5) recorded with this systems were analyzed by using an analogue type band-pass filter.<br>The spectrum thus evaluated was found not to have any fiat portion at longer period, but to have plausible peak regardless of the spectra for P, S wave groups and maximum amplitudes. The frequency corresponding to the peak of spectrum varies merely with the magunitude of earthquake, but not with the layered structure beneath the station nor with the focal distance. The peak frequency, therefore, may be related to some of the source parameters. Another interesting fact is that the shape of the spectrum becomes broader with the earthquake magnitude, that is, the half-value width, for example, is widening with inceasing magnitude.

収録刊行物

  • 地震　第２輯

    地震　第２輯 26 (4), 336-347, 1973

    公益社団法人 日本地震学会

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